Radar apparatuses using radio signals include a radar apparatus using FMCW (Frequency Modulated Continuous Wave) signals. The radar apparatus transmits an FMCW signal, and receives, as the received signal, the FMCW signal returned as it is reflected by an object. The radar apparatus multiplies the received signal by the transmission signal to generate a multiplied signal. The frequency of the multiplied signal is determined by the time difference between the received signal and the transmission signal. Hence, the radar apparatus measures the distance to the object, its relative speed, or the like by generating the multiplied signal. For accurate measurement, the FMCW signal needs to change its frequency almost linearly with respect to the time.
There is conventionally proposed a method of converting the frequency of the output signal from a voltage-controlled oscillator into a voltage, comparing it with an externally input voltage signal with a triangular waveform, and controlling the voltage-controlled oscillator using the error between them, thereby generating an FMCW signal having high linearity (for example, JP-A 2008-224350 (KOKAI)).
When a voltage-controlled oscillator, frequency-voltage converter, operational amplifier, and the like are used for FMCW signal generation, as in the above-described method, these circuits generate noise, and this leads to phase noise in FMCW signals. The phase noise degrades the characteristics of the FMCW signals.